I have searched the internet for a solution to the question above but have had no luck up to now. I have been producing a number of 2D plots where the origin of (0,0 point) is represented by an image. I have made these by plotting the data on an image, where the image is all white apart from the desired symbol at the center point (so I can reshape it as needed). I then move the axis so they cross at the center point. This all works fine, but I now have to create a number of plots using ‘fill’ to place two shaded areas on the plot that overlap in the center. This causes the symbol to be difficult to see even using ‘alpha’.
I therefore have two options to get the desired effect, both requiring me to put an image on top of the figure after the data is plotted. These options are:
1) I place the image on top of the plot and apply alpha to it (May not look very good as it will mute the plot).
2) The better option would be to crop the image around the symbol and then position it on top of the plot so the image center is at the origin (I have no idea how to position the image this way).
Both methods need the image to be placed on top of the plot after the data is plotted. I have tried 'hold on' and calling 'figure(imagesc(Image))' neither work. I have Matlab 2012b but no toolboxes (so cannot use subimage etc.)
Thanks for any help you can give
You can set the transparency of individual pixels of an image using the 'AlphaData' option. So, you can plot the overlay as follows:
% plot your data normally
...
hold on
% assuming the overlay is a 11x11 image
image(-5:5,-5:5,image_matrix,'AlphaData',alpha_matrix);
image_matrix would obviously be the matrix with your image data stored in it, while alpha_matrix would be a matrix of the same size as image_matrix. Every pixel you want to show would have a value of 1, every pixel you want to hide (the white pixels) would be 0.
Related
Firstly, many apologies if this question has been posted/asked/answered (let me know the link if that is the case).
How do I capture the HOG values displayed/plotted on the visualisation figure in Matlab?For example in this link (Matlab) https://uk.mathworks.com/help/vision/ref/extracthogfeatures.html
img = imread('cameraman.tif');
[featureVector,hogVisualization] = extractHOGFeatures(img);
%Plot HOG features on the original image
figure;
imshow(img);
hold on;
plot(hogVisualization);
What I don't understand is when I open 'hogVisualization' in matlab the values which are plotted in the image don't make sense. Where can I find the values plotted on the original image?
To be more specific, here is what I'm trying to do. In this image here > phase I'm trying to detect the lines in the red region (I can detect these lines). However, as you can see these lines are disconnected in the blue region. In my algorithm, I need to track which direction I should go (e.g. to the left, right or to a certain angle direction) when it reaches the disconnected line.
For this purpose, I used HOG to find the orientation. Visually, I can see the correct orientation when I visualise it, which can be used to connect two disconnected lines within the blue region. But the problem is I need to find the values plotted in the image. How do I get these values? I can see them visualised on the image but I can't retrieve the actual numerical values.
Thanks,
Erick
As an input of my code, I need to have some positions on my picture: the positions are in pixels and the origin (0,0) is in the CORNER top left of my picture
The problem is that when I run my code which maps the positions on my picture, the origin shifts to the bottom left :
So my question is : how could I also shift my input (positions of my picture1) so that it is relevant with the code process?
Thank you for your help,
Aude
Adding an answer with a bit detail:
In computers, image processing etc it is the norm to have the (0,0) pixel in the top left corner. However, it is understandable that when you have x,y data, you'd want to plot it together with the image. Here some solutions:
imshow(image);
axis xy; % This line sets up the axis in a standard coordinate system
you can revert it with axis ij
Often, this is not enough. As imshow assumes that each pixel is in integer index position, and you may not have that. Maybe your data is in milimeters, or in any other arbitrary units. A solution to that is using imagesc
imagesc(img);
is equivalent to imashow(img);axis xy. Additionally, you can choose arbitrary matrices for pixel locations as imagesc(x,y,img);
Finally, you can flipud your data for plotting, but I suggest you do that inline with the plot, so you dont modify the data itself.
imshow(flipud(img))
With images you reverse the Y axis:
set(ax,'YDir','reverse');
That would depend on your code. Maybe you can do it on-the-fly so you'll get the desired output right away.
If not just flip the output. You could use flipud for that.
https://de.mathworks.com/help/matlab/ref/flipud.html
I'm making a GUI (with GUIDE) in which there is an axis used to display image sequences. In order to let the user select a region of interest in the sequence I'm using 'imrect'. The problem is the following: everything goes fine when images are smaller than 512x512 pixels (approximately), however for larger images (I tried 600x600 and 1024x1024) the rectangle does appear, I can change its size but I can't drag it around. I though it had to be with axis units so I changed the property from 'pixels' to 'normalized' and use normalized coordinates, but it does not work.
Here is my code to create the rectangle and restrain its movement to the axis limits:
hROI = imrect(hVideo,[Width/4 Height/4 Width/2 Height/2]; % Arbitrary size and position of the rectangle, centered on the image.
fcn = makeConstrainToRectFcn('imrect',get(gca,'XLim'),get(gca,'YLim'));
setPositionConstraintFcn(hROI,fcn);
When I perform the same operation on those large images outside the GUI it works. Any hint is welcome!
thanks
I found a workaround to the problem, in case it can help someone:
In the call to imshow just before calling imrect, we need to specify the axis limits as the "XData" and "YData" parameters.
Example:
imshow(Movie{Frame},'parent',handles.axes1_Video,'XData',get(gca,'XLim'),'YData',get(gca,'YLim'))
It works for images up to 1024x1024.
Simple rounded corner rectangle code in Matlab can be written as follows.
rectangle('Position',[0,-1.37/2,3.75,1.37],...
'Curvature',[1],...
'LineWidth',1,'LineStyle','-')
daspect([1,1,1])
How to get the x and y coordinates arrays of this figure?
To get the axes units boundaries, do:
axisUnits = axis(axesHandle) % axesHandle could be gca
axisUnits will be an four elements array, with the following syntax: [xlowlim xhighlim ylowlim yhighlim], it will also contain the zlow and zhigh for 3-D plots.
But I think that is not what you need to know. Checking the matlab documentation for the rectangle properties, we find:
Position four-element vector [x,y,width,height]
Location and size of rectangle. Specifies the location and size of the
rectangle in the data units of the axes. The point defined by x, y
specifies one corner of the rectangle, and width and height define the
size in units along the x- and y-axes respectively.
It is also documented on the rectangle documentation:
rectangle('Position',[x,y,w,h]) draws the rectangle from the point x,y
and having a width of w and a height of h. Specify values in axes data
units.
See if this illustrate what you want. You have an x axis that goes from −100 to 100 and y axis that goes from 5 to 15. Suppose you want to put a rectangle from −30 to −20 in x and 8 to 10 in y.
rectangle('Position',[-30,8,10,2]);
As explained by the comments there appears to be no direct way to query the figure created by rectangle and extract x/y coordinates. On the other hand, I can think of two simple strategies to arrive at coordinates that will closely reproduce the curve generated with rectangle:
(1) Save the figure as an image (say .png) and process the image to extract points corresponding to the curve. Some degree of massaging is necessary but this is relatively straightforward if blunt and I expect the code to be somewhat slow at execution compared to getting data from an axes object.
(2) Write your own code to draw a rectangle with curved edges. While recreating precisely what matlab draws may not be so simple, you may be satisfied with your own version.
Whether you choose one of these approaches boils down to (a) what speed of execution you consider acceptable (b) how closely you need to replicate what rectangle draws on screen (c) whether you have image processing routines, say for reading an image file.
Edit
If you have the image processing toolbox you can arrive at a set of points representing the rectangle as follows:
h=rectangle('Position',[0,-1.37/2,3.75,1.37],...
'Curvature',[1],...
'LineWidth',1,'LineStyle','-')
daspect([1,1,1])
axis off
saveas(gca,'test.png');
im = imread('test.png');
im = rgb2gray(im);
figure, imshow(im)
Note that you will still need to apply a threshold to pick the relevant points from the image and then transform the coordinate system and rearrange the points in order to display properly as a connected set. You'll probably also want to tinker with resolution of the initial image file or apply image processing functions to get a smooth curve.
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Possible Duplicate:
How do I edit the axes of an image in MATLAB to reverse the direction?
The colour image is plotted using the image function based on some information obtained using imread function and for the white and blue image basically I am selecting the coordinates of the heat point(red and blue and their variations basically) from the map and then displaying them using plot function. The problem is that the plotted values are reversed on the Y axis and I can't figure out how to reverse the Y axis of the plot in order to obtain the same correlation between the images.
Could you please explain me how to solve this problem?
By default, matlab draws graphs with (0,0) at the bottom left corner. However, it draw images with (0,0) in the top-left corner.
You can change the image axes to standard bottom-left origin by using the command
axis xy;
Remember to make sure that your image is the currently selected figure.
Use rot90() to rotate the matrix, or a combination or fliplr() (flips matrix, left and right) and flipud() (flips matrix up and down) that produced the heat map image.
If you are plotting an image and you don't want to see the axis tic marks you can turn them off with
axis off
if you are interested in changing the direction of either the x-axis and/or y-axis in an axes handle-object, you can use the set function as follows
set(axesHandle,'XDir','rev','YDir','rev')
where you use XDir or YDir (or both) based on the axis you want reversed.